The present invention relates to a rigging component of "thimble-shackle" type.
It is very commonplace, especially on a pleasure sailing craft, to secure a rope to an object by means of a shackle, in particular to secure a halyard to a sail.
Such a shackle includes a U-shaped body, of substantially uniform diameter, the parallel arms of which are extended by two coaxial rings at their free ends. These rings receive a pin which closes the shackle, it being possible for this pin to be immobilized either by screwing, one of the rings then being tapped, or by the engagement of a notch arranged on the pin in a corresponding indentation arranged on one of the rings. On a pleasure sailing craft the shackles have a body of diameter generally ranging from 3 to 8 millimeters.
Some ropes secured with these shackles, in particular the halyards, may be subjected to great and prolonged tensile stresses. The diameter of the shackles is relatively small in relation to that of the rope, and this results in an effect of shearing of the rope in cases where tensile stresses are great and prolonged. This shearing effect can halve the breaking threshold of the rope.
Further more the rubbing of the rope against the shackle is concentrated on a limited stretch of the rope, which is precisely that destined to be subjected to this shearing effect. The wear which results therefrom contributes to the risk of the rope breaking well before its maximum strength threshold.
To overcome this great disadvantage it is usual to form a bight at the end of a rope by means of a splice, and to place a thimble inside this bight. This thimble has a radius of curvature which is sufficient to eliminate the abovementioned shearing effect and is made of metal or synthetic material capable of withstanding the repeated rubbing against the shackle.
However, the disadvantage of these splices is that they are relatively lengthy and costly to produce. In addition, some ropes of braided form, frequently employed for the halyards in view of their resistance to stretching, cannot be spliced and therefore cannot receive such thimbles.
In addition, thimbles and splices have relatively large lengths, which are added to those of the shackles. In some cases this length, which is necessary for securing the rope, may be a hindrance, for example in the case of a mainsail halyard, since it can restrict the possibilities of sweating-up.
There are rigging components known as "thimble-shackles", made as a single forged or cast component, like a conventional shackle, in which the rounded part of the shackle includes side bulges at the base of the rectilinear arms and, between these bulges, has a diameter larger than that of the remainder of the body.
These side bulges demarcate a groove intended to receive the rope, and the widened diameter of the shackle at this groove increases the radius of the rope winding, and this allows the shearing effect to be limited.
Such a thimble-shackle has the disadvantage of requiring a specific forging or casting tooling which is costly to manufacture. In addition, this thimble-shackle is bulky and heavy, which is hardly desirable, bearing in mind the slatting to which the sails can be subjected. It is also particularly costly as a result of its process of manufacture and of the additional material which it includes.
These weight and cost requirements, as well as the constraints due to the casting work, further restrict the shapes which this shackle can be given, especially with regard to the diameter of the bottom of the groove and the dimensions of the abovementioned side bulges.
Furthermore, these thimble-shackles include a transverse shank, substantially halfway along their body, intended to prevent the rope from moving too far away from the groove in the event of the tension being released, and from rubbing on the remainder of the shackle body. Were such a transverse shank to be lacking, the shackle could pivot in relation to the rope and the pull would be applied out of line.
Fitting this shank in position involves piercing holes in the body of the shackle and then inserting and securing the shank, which is relatively complex and costly to carry out.
In addition, the appearance of the existing thimble-shackles is not very attractive and does not allow them to be easily picked out from a collection of shackles when these are of different sizes.